1. Field of the Invention
This invention relates to photographic cameras of digital exposure control structure, and, more particularly, to a system for setting an exposure control factor such as a shutter speed or aperture value into the camera in the form of a digital signal, while manually operating a single button.
2. Description of the Prior Art
It is known to set an exposure control factor into a camera in the form of a digital signal, as, for example, disclosed in U.S. Pat. No. 3,928,858 issued Dec. 23, 1975 or German Laid-Open Application No. 2,449,092. The method of this patent necessitates the use of a code plate and contact pins. As the pins are worn out, therefore, the life-time of the camera is shortened. Further, because of the mechanical setting of the camera by the code plate, a complicated exposure control structure results.
On the other hand, it is also known to provide an electrical setting apparatus as disclosed in U.S. Pat. No. 3,748,979 issued July 31, 1973 or German Patent Application Publication No. 2,164,243 issued July 5, 1973, wherein a counter for storing the exposure control factor is connected at its input terminal to the output terminal of an AND circuit having two input terminals, one of which is connected to the output terminal of a pulse generator, and another input terminal which is connected to the output terminal of a photoelectric pulse generator. Thus, the number of pulses dependent upon the width of a pulse supplied from the photoelectric pulse generator is applied to the counter.
However, this pulse width is proportional to the object brightness level as photoelectrically sensed, and, further, the counter is provided with no display unit so that it is impossible to set a desired value of the exposure control factor into the camera.